Phencyclidine (PCP), a major drug of abuse, elicits hallucinations and feelings of tranquility and can generate very aggressive and violent behavior. No specific treatment has yet been devised for its harmful behavioral effects, which are believed to be mediated via specific PCP receptors in the brain. Polypeptides of PCP receptors from rat brain have recently been identified in this laboratory by photoaffinity labeling with (3H)-azido phencyclidine ([3H]AZ-PCP). The aim of the proposed study is to determine the molecular structure of rat brain PCP receptors by the use of (3H)AZ-PCP photoaffinity labeled receptors, and to elucidate the relationship between the structure of these receptors and the psychotomimetic and abuse-promoting effects of PCP. The primary structure of the PCP-binding site once determined, will be used as a model template for the design and synthesis of a PCP-receptor antagonists. The specific aims are: 1. To elucidate the pharmacological properties of (3H)AZ-PCP-labeled polypeptides in various regions of the rat brain and the relationship between these polypeptides and the apparent heterogeneity of PCP receptors. 2. To identify which of the polypeptides, and in which brain regions, undergo alteration in rats that have developed tolerance to PCP upon chronic administration of the drug. 3. To determine the relationship betwen these polypeptides and the ontogenesis of brain PCP receptors. 4. To isolate the three major polypeptides bearing (3H)AZ-PCP binding sites (Mr = 90 K, 62 K and 33 K) by means of conventional chromatographic methods as well as by HPLC followed by preparative two-dimensional gel electrophoresis, and to raise polyclonal antibodies against each of these polypeptides. The antibodies will be used for studies on the homology between PCP receptors and other related receptors as well as for large-scale purification of PCP receptors by immunoabsorption. 5. To solubilize and purify non-denatured brain PCP receptors by affinity chromatography and to determine the molecular structure of the native PCP receptor. 6. To devise a new strategy for drug design. The peptide carrying the radiolabeled ligand will be isolated from an enzymatic hydrolysate of the separated (3H)axido-labeled polypeptides constituting the PCP-receptors. The structure of this peptide carrying the PCP binding site determined by microsequencing will serve as a template for the design and synthesis of various derivatives which will be complementary to the template. This procedure can be expected to result in the synthesis of a "PCP-receptor-antagonist".